The variation in body temperature during menstrual and estrous cycles is one of the prime indices of ovulation and other endocrine changes in the female. This project will examine the mechanisms of the temperature variation. Female rats will be ovariectomized, then treated with estrogens and/or progestogens administered via implanted Silastic capsules which permit sustained hormone release. The animals will be tested for five thermoregulatory responses: behavioral thermoregulation, metabolism, evaporative heat loss, vasomotor activity, and body temperature. Analysis of the pattern and interaction of the response measures will provide information on (a) the mechanisms of heat loss and heat production that underlie the temperature fluctuations of the estrous cycle, and (b) whether these fluctuations are regulated or secondary to changes in one or more of the avenues of heat loss and heat production. Finally, the loci of action of the ovarian hormones will be investigated by CNS or peripheral hormone treatment in ovariectomized, thyroidectomized, and adrenalectomized animals. We suspect that the preoptic-anterior hypothalamic area is a common neural locus for the interaction of ovarian hormones and temperature regulation. Preliminary work has shown that behavioral thermoregulatory responses in particular are very sensitive to ovarian manipulations, and together with the other thermoregulatory responses, will provide basic information regarding thermal variations as a function of reproductive cycles. This information will be valuable in determining the feasibility of using rhythmic temperature variations as a means of birth control.